1. Field of the Invention
The present invention generally relates to a magnetic recording medium, and, more particularly, to a magnetic recording medium used in a magnetic recording and reproducing device employed as an external memory device for an information processing device such as a computer.
2. Description of the Related Art
Conventionally, in regard to a recording layer of a magnetic recording medium such as a hard disk, a technology of combining a perpendicular magnetic film and an in-plane magnetic film has been a frequently studied issue. For example, Japanese Laid-Open Patent Application No. 11-283229 discloses a recording method, in which a perpendicular magnetic film is formed thick, and a recording is performed to the perpendicular magnetic film by using a magnetic head for use in an in-plane recording. This recording method provides an advantage of not necessitating a waveform processing, because this method can obtain a reproduction waveform of the in-plane-recording type, despite being a recording method for a perpendicular magnetic film.
Additionally, Japanese Laid-Open Patent Application No. 5-189737 discloses a method of combining two types of hard magnetic orientation films (a perpendicular magnetic film and an in-plane magnetic film) in which magnetic reversal modes become a domain-wall-transition type and a magnetic-rotation type, respectively, at transition positions (magnetic reversal positions) in a recording state. This method is supposed to contribute to improving an overwrite property and increasing an S/N ratio.
With respect to a magnetic recording medium of a composite type combining a perpendicular magnetic film and an in-plane magnetic film as above, many proposals have been made in regard to a method to perform a recording to the perpendicular magnetic film. However, none of these proposals has made the magnetic recording medium satisfactory enough to be used in a practical level.
Thereupon, with respect to such a magnetic recording medium of a composite type using a perpendicular magnetic film and an in-plane magnetic film, there has recently been a proposal that the in-plane magnetic film be used to function as a recording layer, and the perpendicular magnetic film be used as an auxiliary film to enhance the function of the in-plane magnetic film. It is pointed out that combining the perpendicular magnetic film with the in-plane magnetic film forms a horseshoe magnetization mode that causes a return current in a magnetic field from the in-plane magnetic film, and thus, this magnetic recording medium can achieve an increase in output and a decrease in noise so as to perform a high-density recording.
However, the above-mentioned composite magnetic recording medium using the in-plane magnetic film as a recording layer has problems of the occurrence of noises due to a diamagnetic field at a transition position of the in-plane magnetic film, and a distortion in a reproduction waveform as a result of combining the perpendicular magnetic film to the in-plane magnetic film. So far, no composite magnetic recording medium using the in-plane magnetic film as a recording layer has been devised to have a preferable structure that solves these problems.
It is a general object of the present invention to provide an improved and useful magnetic recording medium in which the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide a magnetic recording medium of a composite type having a perpendicular magnetic film combined with an in-plane magnetic film used as a recording layer so as to decrease noises and prevent a distortion in a reproduction waveform.
In order to achieve the above-mentioned objects, there is provided according to one aspect of the present invention a magnetic recording medium comprising:
an in-plane magnetic film used for recording, the in-plane magnetic film having a magnetization easy axis in an in-plane direction; and
a perpendicular magnetic film formed on the in-plane magnetic film, the perpendicular magnetic film having a magnetization easy axis oriented in a direction perpendicular to the magnetization easy axis of the in-plane magnetic film,
wherein a tBr of the perpendicular magnetic film is set so as not to exceed one-fifth of a tBr of the in-plane magnetic film at the maximum, where the tBr is the product of a thickness and a residual magnetization.
According to the present invention, since the magnetic condition of the perpendicular magnetic film is restricted within a predetermined range, the perpendicular magnetic film sufficiently functions as an auxiliary film to the in-plane magnetic film; thus, the magnetic recording medium can have a composite structure that can restrain a distortion of a reproduction waveform so as to obtain a high S/N ratio.
It is sufficient that the tBr of the perpendicular magnetic film is set so as not to exceed ⅕ of the tBr of the in-plane magnetic film. More preferably, the tBr of the perpendicular magnetic film is set so as not to exceed {fraction (1/10)} of the tBr of the in-plane magnetic film.
Additionally, in the magnetic recording medium according to the present invention, the perpendicular magnetic film may have a thickness not exceeding 5 nm at the maximum.
According to the present invention, the magnetic recording medium can surely restrain the distortion of the reproduction waveform.
Additionally, in the magnetic recording medium according to the present invention, an anisotropic magnetic field Hk of the perpendicular magnetic film may be set at least 1.2 times as large as an anisotropic magnetic field Hk of the in-plane magnetic film.
According to the present invention, a transition position of the perpendicular magnetic film can be arranged to surely coincide with a transition position of the in-plane magnetic film so as to reduce a diamagnetic field likely to occur at the transition position of the in-plane magnetic film; this contributes to decreasing noises.
Additionally, the magnetic recording medium according to the present invention may further comprise a nonmagnetic spacer provided between the in-plane magnetic film and the perpendicular magnetic film.
According to the present invention, the perpendicular magnetic film can be easily formed on the in-plane magnetic film via the nonmagnetic spacer.
Additionally, in the magnetic recording medium according to the present invention, the nonmagnetic spacer may have a thickness not exceeding 2 nm.
According to the present invention, a distance between a magnetic recording/reproducing head and the in-plane magnetic film used as a recording layer can be maintained preferably.
Additionally, in the magnetic recording medium according to the present invention, the perpendicular magnetic film may be formed of one of a Co-group alloy and a Co-group artificial lattice film.
According to the present invention, the magnetic recording medium can have a more preferable perpendicular magnetic film.
In order to achieve the above-mentioned objects, there is also provided according to another aspect of the present invention a magnetic recording and reproducing device including:
a magnetic recording medium comprising:
an in-plane magnetic film used for recording, the in-plane magnetic film having a magnetization easy axis in an in-plane direction; and
a perpendicular magnetic film formed on the in-plane magnetic film, the perpendicular magnetic film having a magnetization easy axis oriented in a direction perpendicular to the magnetization easy axis of the in-plane magnetic film,
wherein a tBr of the perpendicular magnetic film is set so as not to exceed one-fifth of a tBr of the in-plane magnetic film at the maximum, where the tBr is the product of a thickness and a residual magnetization.
The magnetic recording and reproducing device according to the present invention can reduce noises and exhibit an excellent reproduction waveform, and thus can perform a recording with a high density and a high sensitivity.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.